1. Field of the Invention
The present invention relates to a device and a method for holding and securely attaching a linear scale on an object to be measured. More particularly, the invention relates to a linear scale attachment device and attachment method which allow easy attachment to an object to be measured and maintenance of the scale, and which can relieve the effect of thermal stress caused by a difference in thermal expansion coefficient between the linear scale and the object made of a different material from the scale.
2. Description of the Related Art
An attachment device used for attaching a relatively long linear scale such as a glass scale or thin metal tape scale on a machine to be measured generally includes a base that has both functions of holding the scale and fixing the scale on the machine.
Such an attachment device requires to be small and lightweight, and should allow easy attachment to the target machine and maintenance of the scale. Further, the device should have a structure that relieves the effect of thermal stress caused by different thermal expansion coefficients of the materials for the device and the machine. These requirements are particularly important for metal linear scales commonly called tape scales, which can sometimes have an entire length of more than 10 m.
A conventional technique devised to satisfy the above requirements is disclosed in Japanese Patent Laid-Open Publication No. Sho 59-224501. A tape-like scale is inserted into a hollow base from one end in a lengthwise direction. As the scale sometimes cannot be inserted smoothly because of size variation and the like, high-frequency vibration is applied during the insertion of the scale using a vibration generator. Japanese Patent Laid-Open Publication No. Sho 59-138915 discloses a technique in which the scale is pulled from one direction into a similar base using a spring.
Some such attachment devices in practical use are provided with an aluminum base. In some applications, the base may be permanently attached to an iron machine using a screw, or, tacked to the machine using a double-sided tape. Here, the thermal expansion coefficient of aluminum is different from that of iron.
However, when the aluminum base is permanently attached to the iron machine using a screw, the measurement accuracy may be degraded because of thermal stress caused by a difference in thermal expansion coefficient between aluminum and iron. The effect of thermal stress can be reduced by resiliently attaching the scale onto the machine using a double-sided tape, but such tape is inferior in respect to easy attachment or maintenance of the scale, and long-term stability.
Thus, while conventional aluminum bases for holding and fixing scales on an object to be measured are small and lightweight, there still is a scope of improvement for securely attaching a relatively long scale on a machine, such as various problems described above.